298 R. R. BENSLEY 



4. Effect of inanition on the number of islets in the pancreas of the dog. . 337 

 Relation of the islets of Langerhans to the ducts and acini of the pancreas. . . 340 

 Structure of the pancreatic epithelium 354 



1. The cells of the pancreatic acini 355 



2. The structure of the islet-cells 364 



3. The structure of the epithelium of the intralobular ducts and of the 



centroacinous cells 371 



Transitions between acinus cells and islet cells 372 



Bibliography 387 



INTRODUCTION 



Since the discovery by von Mering and Minkowski in 1890 

 that complete removal of the pancreas was followed in dogs by a 

 rapidly fatal diabetes, the interest in the pancreas as an organ 

 of internal secretion has been extreme. Laguesse, in 1893, on 

 anatomical grounds, came to the conclusion that the islets of 

 Langerhans were engaged in internal secretion, and Schaefer 

 ('95) suggested that in diabetes lesions would probably be found 

 in these structures. Since that time an immense literature of 

 investigation has grown up in which one might expect to find 

 answers to the perplexing questions which have arisen concerning 

 the relations to one another of the various histological elements 

 which compose the pancreas. It is not the purpose of this paper 

 to give a resume of this literature, for that has been well done in 

 the recent summary made by Laguesse ('06-'08) in the Revue 

 d'histologie generale. It will suffice here to point out some feat- 

 ures in which there are still considerable differences of opinion 

 and to indicate as far as may be possible the reasons of this dis- 

 agreement. 



The differences of interpretation of the islets of Langerhans are 

 well known. To the majority of histologists they are structures 

 which, though originating from the pancreatic anlage in enibrj'- 

 onic life, yet maintain a separate existence and full specificity. 

 Others regard them as temporary phases in the history of the 

 acini of the pancreas, denying them any special function, while 

 still others believe that they represent products of change of the 

 acinus cells, performing, however, a special function of internal 

 secretion while in the islet condition. 



When we come to consider questions of anatomical fact rather 

 than of interpretation it is more surprising that there should be 



